Experimental cookery

tributed in plants, usually as the calcium salt, and apparently less fre- quently as the sodium and potassium salts. It has rarely been detected as the free acid. The calcium salt is precipitated on adding calcium acetate to a solution of the acid. Calcium oxalate is insoluble in acetic acid, but soluble in dilute mineral acids." It is found in the rumex or dock family, of which different docks and sour grass are used as food. Sorrel and rhubarb contain a rather high percentage. Rider has reported the most extensive determinations of oxalic acid in leafy vegetables. She has found that the amount in spinach ranges from 0.486 to 0.692 per cent. Beet greens give an equivalent or slightly higher amount than spinach, and New Zealand spinach contains a still higher percentage. No oxalic acid w^as found in dandelion greens, kale, turnip greens, and mustard greens. McLaughlin has reported the oxalic acid content of eight samples of New Zealand spinach as ranging from 0.49 to 0.53 per cent, anhydrous. As these figures indicate, the amount in different samples of the same vegetable may vary. Rider mentions this fact in connection with the samples she analyzed. Nelson has reported 0.31 per cent oxalic acid in spinach. Succinic acid is found in many plants, and glutaric and adipic have been isolated from the sugar beet. Malic acid is found as the free acid and as the salts of malic acid in many plants, and particularly in apples and pears. Citric acid is found in tomatoes and it is found in smaller quantities in other foods. Blunt reports small amounts in cabbage, asparagus, and string beans. Nelson has reported that spinach contains both citric and malic acids. The ratio of citric to malic acid in broccoli was 3 :2. The leaves and buds contained approximately the same proportions. Small amounts of oxalic and succinic are also present. The acid content of lettuce was as follows: oxalic, 1 -malic, and citric, 0.011, 0.065, and 0.048 per cent respectively. Tomatoes, which have the highest amount of acid of our common vegetables, contain citric acid. Blunt reports 0.42 per cent. The acids found in fruits. Conflicting reports appear in the literature regarding the particular acid in different foods. Bigelow and Dunbar sug- gest that this is due to the inaccurate methods of analysis often used and to the difficulty in separating the different acids from one another. Nelson has reported the approximate percentages of the various acids in fresh fruits, the average total acidity being calculated as citric. His results are given in Table 15. Nelson states that the most common acids in fruits, citric and malic, may occur in different proportions or one alone may be present. "The total acidity of most fruits varies with the variety and the degree of ripe- ness. The relative proportions of the various acids may also vary with the degree of ripeness, variety, and climatic and soil conditions." Rhubarb contains some oxalic acid ; cranberries and plums some benzoic. Other acids sometimes found in small quantities are succinic, lactic, iso- ACIDS FOUND IN FRUITS 109 TABLE 15 The Acids of Fruits {Nelson) Fruit In- ves- ti ga- tor Cit- ric % Mal- ic % Tar- tar- ic % Ben- zoic C7 /O Oxal- ic % Suc- cin- ic % Lac- tic % Iso- cit- ric % Total acidity (titrat- able) % Apple (Winesap) Apricot (dried) Banana N N P